1. Field of the Invention
The present invention generally relates to an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction device, that includes a development device.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, or multifunction devices including at least two of those functions, include an image carrier on which an electrostatic latent image is formed, a development device to develop the latent image with developer, and a transfer unit to transfer the developed image from the image carrier onto a sheet of recording media.
The development device is a mechanism that typically includes a developer carrier (developing sleeve) on which the developer is carried, a developer circulation path (developer transport path) in which the developer is circulated, and a developer transporter (e.g., a screw) to transport the developer in the development device.
As the developer, two-component developer including toner and carrier is widely used. It is to be noted that the term “two-component developer” also refers to developer including an additive and the like in addition to the toner and the carrier. The developer should be replaced as the toner is consumed and the carrier deteriorates over time, and various approaches described below have been advanced to remove the deteriorated developer (that is, used developer) from the development device automatically during maintenance work or the like. More specifically, when the developer is replaced, the development device is driven while being set on the image forming apparatus to discharge the used developer therefrom, after which the development device is filled with fresh developer.
In a known development device, to replace the developer, the used developer is carried on the developing sleeve, and a regulator that contacts the developing sleeve scrapes the developer off from the developer sleeve and into a container.
In another known development device, the developer circulation path includes a developer discharge port that is openably closable with a shutter that, when opened, enables the used developer to be discharged from the development device through the developer discharge port.
In yet another known development device, the developer discharge port is disposed close to the developer circulation path. The used developer is discharged from the development device through the developer discharge port while a developer transport screw is rotated in both a normal direction and a reverse direction.
However, in the known development devices described above, when multiple developer transport paths (e.g., an upper transport path and a lower transport path) are arranged vertically to circulate the developer within the development device in an axial, longitudinal direction of the development device, the developer tends to accumulate in a downstream portion in the lower transport path in a direction in which the developer is circulated (hereinafter “developer transport direction”), and cannot be fully removed from the development device.
More specifically, the developer accumulated in the downstream portion of the lower transport path in the developer transport direction is pushed up to an upstream portion of the upper transport path. If the openably closable developer discharge port is disposed in the lower developer transport path, when the amount of the developer in the development device decreases as the used developer is discharged through the developer discharge port, the developer remains in a portion between the developer discharge port and the downstream portion of the lower transport path while it is not transported from the lower transport path to the upper transport path. While the developer in the lower transport path is not sent to the upper transport path, because the developer is packed in the downstream portion of the lower transport path with the transport force of the developer transporter, the developer coagulates. That is, after the automatic removal of the developer is finished, the coagulated toner remains in the development device, which is undesirable. In particular, if unused toner is added to the development device including the toner coagulation and then image formation is performed, it is possible that output images include the coagulated toner, that is, image failure occurs.
In view of the foregoing, there is a need for a simple and effective way to remove the toner fully from the development device during automatic removal of the developer, which the known development devices fail to do.